Doherty Peaking Amplifier Feedback for Phase-Stable Gain Control
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Solution Overview
Problem
In Doherty amplifier circuits, changes in the bias point of common-emitter amplifiers lead to significant alterations in input impedance and transmission phase characteristics, affecting the phase relationship between carrier and peaking amplifiers, resulting in distortion of radio-frequency output signals.
Innovation Solution
Incorporating a feedback circuit with a resistor and capacitor in the peaking amplifier, which provides a voltage or current based on the amplified radio frequency signal to the transistor, stabilizing characteristics by increasing feedback amplitude and reducing the impact of parasitic capacitance, thereby maintaining consistent phase difference between carrier and peaking amplifier outputs.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If the bias point of the peaking amplifier is changed to control gain, then the gain control capability is improved, but the transmission phase characteristics and input impedance change significantly, causing distortion of the radio-frequency output signal
Solution Approach 1:
The patent applies feedback by introducing a feedback circuit that provides a voltage or current based on the amplified radio frequency signal back to the transistor's base, gate, emitter, or source. This feedback mechanism stabilizes the transmission phase characteristics and input impedance of the peaking amplifier when the bias point changes, preventing signal distortion while maintaining gain control capability.
Solution Approach 2:
The patent utilizes parameter changes by deliberately adjusting the bias voltage or current of the transistor to control the gain of the peaking amplifier. By changing the bias point parameter, the amplifier can adapt to different gain requirements while the feedback circuit ensures that other critical parameters (phase characteristics and input impedance) remain stable.
2Reliability
If feedback circuit is introduced to stabilize characteristics, then the transmission phase stability is improved, but the device complexity increases
Solution Approach 1:
The feedback circuit is implemented with minimal additional components (resistor and capacitor) connected to the existing transistor terminals. The feedback voltage or current is derived directly from the amplified radio frequency signal at the collector or drain, requiring no additional signal sources or complex control circuits. This simple feedback structure stabilizes transmission phase characteristics while adding minimal complexity to the overall amplifier circuit.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The solution effectively suppresses changes in input impedance and transmission phase characteristics, preventing distortion of the radio-frequency output signal across varying input and output powers, ensuring stable amplifier performance.
Implementation Method 1
The feedback circuit provides, to the base or gate or an emitter or source of the transistor, a voltage or a current based on the amplified radio frequency signal
Data Source
AI summary
A Doherty amplifier circuit includes a carrier amplifier including one or more amplifiers, and a peaking amplifier including one or more amplifiers. At least one of the amplifiers includes a transistor and a feedback circuit. The transistor receives, at its base or gate, a radio frequency signal and a bias voltage or current which changes, and outputs an amplified radio frequency signal from its collector or drain. The feedback circuit provides, to the base or gate or the emitter or source of the transistor, a voltage or a current based on the amplified radio frequency signal.